Brush for electrical machines



CUAIINU UH ILPDI'U Patented Oct. 2 5, 1932 att UNITED STATES PATENT OFFICE RALPH L. SEABURY AND LOUIS W. MURRAY, E ANDERSON, INDIANA, ASSIGNORS TO DELCO-REMY CORPORATION, OF ANDERSON, INDIANA, A CORPORATION OF DELA- WARE no Drawing.

This invention relates to brushes for electric machines and the method of making such brushes.

One object of the invention is to provide a brush in which a more homogeneous and intimate mixture of the materials forming it is secured than heretofore whereby brushes of more uniform quality are obtained.

. Another object of the invention is to provide a brush in which a lesser quantity of the binder is employed than has been heretofore used in brushes of the desired quality.

It is a further object of the invention to provide a brush containing a metallic constituent, having increased conductivity and containing metal in substantially pure metallic state.

It is another object of the invention to devise a method of making brushes having the properties above referred to which is simple and easy to carry out; is inexpensive and safe; and by means of which brushes having a meta lic constituent can be formed without the formation of metallic oxide and which have greater conductivity than those made by methods heretofore used.

- This application relates to a specific method for forming brushes for electrical machines and is an adaptation of a method for mixing granular materials which is described and claimed broadly in applicants copending application Serial No. 458,591.

Heretofore, brushes for electric machines have been made primarily by one or the other of two methods. The materials which constitute the brush such as gra l 1 ite and a bind- 'er'oil bglr elite or some snni ar compound are mixed together dry in powdered form and are then formed into the desired shape in a briquetting press after which theyare heated to cure the binder. If a binder such as pitch is employed, the binder is usually added in? liquid form and is mixed with the graphite until the whole becomes a stiff paste subse'f fient to which it is molded under pressure as above described. A relatively large amount of the binder must be used if the materials are mixed dry because it is diflicult Y to secure a uniform mixture with a small amount of the binder, resulting in a part BRUSH FOR ELECTRICAL MACHINES '3 2 5 Application filed lay 31, 1930. Serial No. 458,590.

of the mixture having a greater proportion of binder than other parts and in the formation of a variable product. In order to secure a better mixture, another method has been employed in which the binder is dissolved in a volatile solvent such as aleoh ql or benzol which lsfiixe'd' with the raphite. TlllS solution of the binder is then'i fiid'd to the graphite, and the whole is mixed and the solvent is then evaporated. While this process has proved reasonably satisfactory, so far as the mixing operation is concerned, it is expensive due to the loss of the solvent and presents a dangerous fire hazard because of the use of large uantities of the solvent.

According to t e present invention a method has been devised which is effective to secure an exceedingly homogeneous mixture of the materials employed and which is neither expensive nor dangerous. This method contemplates the mixture of the graphite in a wet condition with a flution of the binder in caustic alkali y T he amount of binder necessary to produce satisfactor brushes when the materials arev mixed in t is manner is variable within certain limits. Most excellent brushes have been made containing from fifteen parts balgelite and eighty-five parts graphite, to eight'p'arts bakelite and ninety-two Farts graphite, in fact,,as little as four percent of bakelite has been employed with very satisfactory results. The ra hite is mixed with waterthoroughly in any suitable mixing device tdmake a relatively thin paste and to this is added a solution of bakelite in some alkali such as so mm 11362531156; otasslum h droxide, calcium H droxi e, so mm car ona (a) sodlum silicate 1n act, almosthn'y alliali may Be used with the exception of ammonium hydroxide which 00 does not give en ire y sa 1s actory results. A f

three to ten percent solution of the alkali may be used and a five percent solution has been found to give excellent results. The amount of alkali necessary to dissolve a given quan- 9 tity of bakelite Wlll vary somewhat, depending on the alkali used, but if sodium hydroxide-is used, about one gram is employed for evarly five grams of bakelite. 4

e bakelite solution is thoroughly mixed 10 a hite and co r. fiorm of the inventlon, e bakelite an with the graphite in any desirable way and the mixture is then treated with suflicient acid such as h drochloric or tralize the solution. 'l he a y 1 ion 0 the acid precipitates the. bakelite from the solution in the form of a ligii tifiid flpfiy curd which costs the graph e partic es on a sides and adheres thereto, water and a salt in s. "ition constituting the residue. The mixture tained is then filtered and washed in any suitable manner to remove the salt and any other impurities which ma be resent. The mixture of graphite and ake ite is then dried in the air (Tin any suitabwdfyer wherethdtinperature is not permitted to go above 200 F., and ground in a suitable mill to form a pow-- der. The powder is then briquetted in a briquetting ress and the bri uettes cured under hear, an pressure in a ba elite mold as is customary in the manufacture of brushes.

It will be understood that when emplo ing the bakelite in an alkaline solution, t e ste of wetting the gra hite may be omitted an the raphite used ry. However, as explained ereinafter, the mixture is not quite so good when d graphite is used and a larger amount of bake ite must be used to secure the same binding efiect.

According to another form of this invention cop' r owder ma be incorporated in the brus ne examp eof the proportions f f th; materials femployed v vyhighkhlave been oun to e satis acto is 8 0 a e ite 32% W Acme this aphite are mixed in the manner previous y described and the mixture is dried'and uloverized, dry copper powder being adde to the dry powdered 'mixture of graphite and the binder. The copper and graphite-binder powder is thoroughly mixed in any suitable way, the mixture is molded-in a bmtlgttiij pressto the desired form and the forms cure 4 in a bakelite mold in the conventional manner.

The addition of metallic copper powder to the brush gives it greater conductivity and moreover, when the co per is mixed with the other ingredients in t e manner above described, the conductivity of the brush is greater than if the copper were mixed with the graphite before the binder is added. When the copper powder is added subsequent to the mixing of the graphite and bakelite, the

small co per articles do not become surrounded y a fi m of the binder to as great an extent as when the binder is added to a mixture vof copper and graphite. -When the graphite and the binder are mixed according j to the present method, the binder adheres so firmly to the graphite that very little of the binder is available to coat the copper particles and the latter are distributed throughout the brush very largely in metallic contact with each other, while according to the earlier process the binder is efi'ective to. coat the copsul huric to neu pure metallic 'co marked increase in con uctivity of the formed brush.

Brushes formed according to this method not onlfy need less copper to 've the same degree o conductivity than 0 brushes made according to methods heretofore employed, but if the copper powder is added to the m xture of bakellte and gra 'hite after the latter has been formed and ried, the formation of co per oxide is substantially prevented and the finished brush contains substantially er. If the copper were addedto the grap ite before mixture with the binderthe subsequent wetting and heating would oxidize the cop 'r.

Another form of t 's invention contemplates the method of mixing the graphite and whiletfiegraphite is in a wet condition. According to this form of the invention, the

a bite is mixed with wagr thoroughly in quantities suflicient to form a relative y stifl' paste, and the binder, such as rosin, pitch or and the dissolved binder is added in smal amounts at a time, while the mixer is operated. The binder curdles when it comes in contact with the wet graphite and spreads over or coats the gra hite particles. The

operation is continue until the (proper amount of the binder is added to an thoroughly mixed with the phite, after which the mixture is dried ei er in air at normal room temperature or in a suitable dryer at a temperature of not to exceed 200 F., for about a day. The dry mass is then pulverized and passed through a screen of about No. 30 mesh after which the powder is molded into brushes in the usual manner in a suitable press under pressure of about twenty tons per square inch if no heat is applied during the molding operation. If heat is employed, the molding may be effected at a lesser pressure. The brushes are then cured and coked if desired in the manner previously described. When the materials are mixed in this we although a volatile solvent is employed, muc less of the solvent is used to wet the materials and secure an intimate mixture because the graphite is first wet with water. Hence, the fire.hazard. is largely eliminated.

Another advantage of wetting the graphite so the binder dissolved ina -volatile solverrt,

'- to 0R PLAsuc is due to the fact that the binder is not absorbed in the pores of the graphite particles when the materials "are mixed in this manner. Owing to the fact that the pores are already filled with water, the binder does not enter these pores but remains on the outer surface where, of course, its binding action is greater than if some of the binder were absorbed. Therefore, a lesser quantity of the binder is necessary. K

While the form of embodiment of the present invention as herein'disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. The method of forming a brush for electric machines which consists in forming a solution of a binder material in an alkali, mixing such solution with graphite,'adding acid to precipitate the binder material from solution on the graphite, filtering, washing and. drying the mixture thus formed, pulverizing the dried material, briquetting such material in the desired form, and curing the forms under heat and pressure.

2. The method of forming a brush for elec- .tric machines which consists in forming a solution of a binder material in an alkali, mixing such solution with graphite, adding acid to precipitatethe binder material from solution on the graphite, filtering, washing and drying the mixture thus formed, pulverizing the dried material, briquetting such material in the desired form, curing and coking the forms.

3. The process of forming a brush for an electric machine comprising, graphite and a suitable binder which includes the steps of forming a solution of the binder in an alkali and subsequently mixing said binder with the graphite.

4. The process of forming a brush for an electric machine comprising, graphite and a suitable binder which includes the steps of wetting the graphite with water forming an alkaline solution of the binder and adding such solution to the wet graphite.

5. The process of forming a brush for an electric machine comprising. graphite and a suitable binder which includes the steps of wetting the graphite with water, disso viug the binder in a 3 to -10 per cent solution of an alkali, adding this solution to the graphite and mixing therewith.

6. The process of forming a brush for an electric machine comprising, graphite and a suitable binder which includes the steps of dissolving the binder in a 3 to 10 per cent solution of sodium hydroxide, using sufiicient of the solution to contain one part by weight of the hydroxide to every 5 parts of the binder rial mixed with raphite which consists in wetting the grapliite with 'water forminga solution of the binder material in a volatile solvent such as alcohol or benzol, mixing such solution with the wet graphite, drying the mixture to evaporate the volatile solvent, ulverizing the residue to obtain a powder w iich is a mixture of graphite and the binder, briquetting the powder in the desired form and curing the forms under heat and pressure.

8. The process of forming a brush for an electric machine comprising, a binder material mixed with graphite, which includes the steps of wetting the graphite and subsequently mixing therewith a solution of the binder material in a voltatile solvent.

9. The process of forming a brush for an electric machine comprising, a binder material mixed with graphite, which includes the steps of wetting the graphite and subsequently adding thereto a relatively concentrated solution of the binder material in a volatile solvent.

10. The process of forming a brush for an electric machine comprising, a binder material mixed with graphite, which includes the steps of wetting the graphite with suflicient water to form a relatively stilt paste andsubsequently mixin therewith a solution of thebinder material in a volatile solvent.

11. The process of forming a brush for 'an electric machine comprising, a binder material mixed with graphite, which includes the steps of wetting the graphite with sufiicient water to form a relatively stifi paste and subsequently mixing therewith a concentrated solution of the binder material in a volatile solvent.

12. The process of forming a brush for an electric machine comprising, a binder ma terial mixed with graphite, which includes the steps of wetting the graphite, subsequcntly mixing a solution of the binder material in a volatile solvent with the graphite and drying the mixture formed in a temperature not in excess of 200 F.

13. The .process of forming a brush for an electric machine comprising, graphite, a binder, and metallic particles. which includes the steps of wetting the graphite, mixing the binder therewith, drying and pulverizing the mixture thus formed, and adding the metallic constituent of the brush subsequent to these operations.

14. The process of forming a brush for an electric machine comprising, graphite, a binder, and metallic particles, which includes the steps of wetting the graphite, adding to the wet graphite and mixing therewith a solution of the binder in an alkali, precipitating the binder from the solution by the addition of acid, drying and pulverizing the mixture thus formed and subsequently adding the metallic constituent of the mixture thereto.

the mass.

In testimony whereof we hereto aflix our signatures.

RALPH L. SEABURY. LOUIS W. MURRAY. 

